Electric squib



Jan. 14, 1941. A BURRQWS ErAL 2,228,339

ELECTRIC sQUIB Filed Nov. 19, 1956 iatented Jan. 14, 1941 x l ELECTRIC SQUIB Lawton A. Burrows and Carl B. Van Winter, Wenonall, N. J., assignors to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware Application November 19, 1936, Serial No. 111,581

. x 7 Claims. (Cl. 102-10) The present invention relates to electric squibs The object of the present invention is a new and to improved ignition compositions for the and improved electric squib.- An additional obl l same. It has particular application to means ject-is a new and improved electric squib such for the prevention of misflres when squibs are that dimculties in series firing are obviated. A

5 fired in series. further object is an electric squib containing a e As is well known, electric squibs are employed slow ignition charge, which may be satisfactorily in igniting delagrating explosive compositions, red in series. Another object is an electric squib for example'black'powderuwhere the nature of containing an improved bridge wire such that the explosive is such that it is desirable to effect misl'lres in series are prevented. Further objects .l initiation by means of a flame rather than by a will be apparent as the invention is hereinafter 1o detonator, as is the case withdynamites and described. f other high explosives. It is common to employ We have discovered that misres in series may electric current for firing the squibs. be practically eliminated by selecting a bridge 'I'he electric squibs known to the art generally wire so characterized that the time required for l consist of a shell or tubeof metal or other matefusion thereof is suiliciently greater Ithan the 1 rial, a defiagrating explosive charge enclosed period of initiation of the charge that certainty therein, and an electrical firing element. The vof ilring in series is. assured. latter element is desirably formed by passing two A possible explanation of the mechanism causleg wires through a mass of insulating material ing misres when squibs are shot in series, is that which closes the shell, and joining the ends of the `circuit is broken before all the ignition 2D these Wires within the shell. The joinder is efcharges therein have been initiated. Orll llrst f fected by means of a highly resistant connectconsideration it might appear that if a squibl ing wire which is heated to `incandescence with would fire alone it would likewise fire in series.

thel passage of electric current therethrough. However, this is not the case. Certain irregu- '25 This bridge wire is imbedded in. the ignition larities invariably occur in the large scale manu- 25 charge so that the passage of current through facture of squibs. It is impossible to maintain the circuit causes the charge to deilagrate. an absolute uniformity in the compositions and When the squib is red thus, the llame plays 'amounts of materials employed. A's a result cerupon the explosive charge to be ignited. tain very minute variations occur in the compo- Delay 'electric squibs differ '1l-om the ordinary sition and structureof the bridge wire, and like- 30 electric squibs in that the firing element is sepwise in the composition of the ignition charge. arated from the chiefdeflagrating charge by a Due to such variations, some bridge wires; supcolumn of material having a uniform rate of posedly uniform, will fuse after a shorter period combustion, .25nd Serving aS a .delay element. of application of the current than the average a5 Electric squibs and delay electric squibs may be wire. some of the ignition charges will require 35 eithervented t0 Provide an esafpe fo? gases, '01' longer than the average time to initiate, due to Yentless t0 k'eep out moisturevariation or segregation of the components The ignitlon composition for electric squibs therein. If such a defective wire happens to be should .possess low and uniform ring Current introduced into the same squib with such an ir- 40 propgrtles' and the ability to develop on com' regular charge, the squib might misflre even if 40 gsl'lya wli qlewgkisgllgngagg' shot alone. But if such a wire occurs in one While many ignition compositions possess one or slrb Ofba'fgroup 'qnnect'ed m series a.nd s.uch athe other of these necessary properties, it is a -c ge 6.5 presen m one or more sqmbs m the 5 fact well recognized in the art that a few are Series mlsres may Occur in the squibs having 45 available which have both of these characteristhe irregular chargef" Whether or not any. m15 es to the desired degree In `admi-,1011, the 1gni lire occurs in the squib having the defective wire. non compositigns in present usey which even ap The effect of ring in series is to combine thel 5 which lead to further dlmculty. Itis generally the irregular charge. As soon as Iche fastest 50 true that compositions which furnish the debridge wire of the series vburns through. the Cirslrable hot flame of considerable duration are cuit, is broken, and any charge in 'the Series,

relatively slow in initiation. 'I'his property rewhich has not Ahad time to be initiated, will results in numerous misnres, when squibs charged suit in a misfire. Naturally such a diiculty will u with such compositions are red in series. e be present chiefly in squibs which employ ignl- 55 wire which is slow to fuse, slow ignition charges desirable for their other qualities may be satisfactorily fired in series without the usual misfires. We prefer to employ for this purpose a wire made from an alloy of nickel and chromium, and having a diameter of approximately 0.00225 inch, Although this type of wire is satisfactory for any squib, it solves the specic problem of the squib which contains an ignition charge capable of initiation by electrical means but which undergoes initiation so slowly that misres occur when such charges are fired in series. We prefer to employ the bridge Wireof our invention in conjunction with what .we shall designate as the slow ignition charge. In order to avoid repetition and preserve clarity, the term slow ignition charge, as used in the specification and claims of this application, is hereby defined to mean, an ignition charge capable of initiation by means of a standard 80% platinum, 20% iridium bridge wire having a diamv eter of 0.0015 inch, but which` undergoes initiation so slowly that misres occur when such charges are fredgin series by meansof such wire.

We have found that the use of a bridge wire which is slow to fuse is particularly advantageous when employed in a squib having our preferred ignition charge comprising a loose blend of ground smokeless powder and black powder. We make no claim to the use of this charge in squibs generally herein, but such is claimed in the cepending application, Serial No. 111,583, filed November 19, 1936, which application has now matured into Patent 2,118,533. A mend of approximately 40% black powder and 60% ground smokeless powder may be used to illustrate the properties of the improved ignition composition. Such a composition is desirable in view of its standardized'ring current of about 0.330 ampere, high rate of deilagration once it has b een initiated, and its hot flame of long duration. When combined with the bridge wire of the present invention, charges of this composition may be fired satisfactorily in series. In addition to the foregoing, it has been found advantageous to employ said bridge wire in squibs containing any suitable slow ignition mixture, -and especially desirable with such loose charges as blends of ground smokeless powder and an oxidizing agent, or ground smokeless powder, an oxidizing agent and at least one nely divided metal. As examples of metals, the following are suitable: aluminum, tellurlum, selenium, zirconium, magnesium and the like. Sulfur or calcium silicide may be substituted for the metals in vthe foregoing, if desired. Any

suitable oxidizing agent may be employed, such as potassium chlorate, potassium nitrate,` barium nitrate, .and barium peroxide. herein to the use of the foregoing'compositions as ignition agents in squibs generally, but such is claimedin copending application, Serial No. 111,582 led November 19, 1936.

In order to describe our invention more clear- Y ly, we-shall refer to the 'attached drawing, which is a view in vertical cross section of an electric No claim is made y squib. The numeral l represents a shell of-any suitable material such as metal, for example, copper, aluminum or the like. At the bottom of the shell is placed a base-charge 2 of black powder, suitably pressed into the shell. This is covered by a loose vslow ignition charge 3. The leg wires 4 are held in position by the plug 5, and are joined by the bridge wire 6, comprising an alloy of nickel and 20% chromium, having a diameter of 0.00225 inch. The squib is closed by means of a waterproofing composition 1, and'a sulfur seal 8. l

It is to be understood that the foregoing embodiment is cited by way of illustration only, and is not to be construed as limiting our invention in any way. While we prefer to employ a squib of the ventless type, the principles of the invention apply equally well to the ventedtype. Although the ordinary electric squib is depicted, our invention is satisfactorily applied to the delay electric squibs, as described inthe foregoing.

As many widelyI different embodiments of this invention may be made, we intend to be limited only by the following claims.

We claim:

1. An electric squib comprising almetal shell, aA

.smokeless powder, an oxidizing agent, and a metal, and charges comprising ground smokeless powder and a black powder, and a'bridge wire comprising an alloy of nickel and chromium having a. diameter of at least approximately 0.00225 inch, whereby certainty of ring is assured under conditions prevailing in series ring.

. 2. An electric squib especially adapted for series ring` comprising a bridge wire and a slow ignition charge., said bridge wire being selecteclA for its cooperation with said ignition charge,.said ignition charge being characterized by a period of initiation atleast equal to that of a standard blend of 40% black powder and 60% ground smokeless powder when the latter is fired with a current of 0.330 ampere through a standard 80% platinum, 20% .iridium bridge wire having a diameter of 0.0015 inch, and said selected bridge wire being characterized by a rupture time substantially in excess of the aforesaid period of initiation of said charge.

3. The electric squib of claim 2 wherein said selected bridge wire comprises' an alloy of approximately 80% nickel and 20% chromium having a `.diameter of 0.00225 inch.

1less powder and an oxidizing agent.

7. The electric squib `of y claim 2, wherein the loose ignition' charge comprises ground smokeless powder, an oxidizing agent, and a metal.

LAWToN A. BURRoWs. CARL B. VAN WINTER. 

